1. Field of the Invention
This invention relates to a method for the hydrolysis of only the lacto-N-biosidic (Gal.beta.1-3GlcNAc.beta.1-) linkage at the non-reducing termini of sugar compounds and provides a reagent for use in hydrolysis by said method.
2. Description of Related Art
Oligosaccharides of glycoproteins and glycosphingolipids change in various biological events, including cancer and cell differentiation. To elucidate the biological functions and structures of these oligosaccharides, exoglycosidases are useful. Various exoglycosidases have been isolated from a number of prokaryotic and eukaryotic sources. However, no enzyme hydrolyzes hetero-oligosaccharides to release disaccharide.
Gal-GlcNAc structures are often found at the non-reducing termini of oligosaccharides. These oligosaccharide structures have been divided into two groups: type 1, with Gal.beta.1-3GlcNAc.beta.1-, and type 2, with Gal.beta.1-4GlcNAc.beta.1-. The N-acetyllactosamine type of sugar chain from several glycoproteins also has type 1 structure (Mizuochi et al., J. Biol. Chem. 254, 6419, 1979; Mizuochi et al., J. Biol. Chem. 255, 3526, 1980; Takasaki & Kobata, Biochemistry 25, 5709, 1986; Townsend et al., Biochemistry 25, 5716, 1986). NMR, mass spectrometry, and methylation analysis have been used to distinguish type 1 and type 2 structures, but much oligosaccharide is needed for the analysis. Another analytical method is .beta.-galactosidase digestion, which requires little oligosaccharide. Diplococcal .beta.-galactosidase specifically cleaves .beta.1-4 galactosyl linkages but not .beta.1-3 or .beta.1-6 galactosyl linkages (Paulson et al., J. Biol. Chem. 253, 5617, 1978). Thus, oligosaccharides hydrolyzed by this enzyme have a type 2 structure, and oligosaccharides not hydrolyzed by this enzyme do not have a type 2 structure. Type 1 structure cannot be identified directly with this enzyme.